Identification of variant molecules of Bacillus thermoproteolyticus ferredoxin: Crystal structure reveals bound coenzyme A and an unexpected [3Fe-4S] cluster associated with a canonical [4Fe-4S] ligand motif

An establishment that V-I and V-II contain the polypeptide of Bacillus thermoproteolyticus ferredoxin (BtFd) associated with acyl carrier protein (ACP) and with coenzyme A (CoA), respectively, and that V-III is a BtFd dimer linked by a disulfide bond is presented. The crystal structure of the BtFd-CoA complex (V-II) determined at 1.6-angstrom resolution reveal that each of the four complexes in the crystallographic asymmetric unit possesses a [3Fe-4S] cluster that is coordinated by Cys(super 11), Cys(super 17), and Cys(super 61).